A known pipe coupling comprises a clamp arrangement incorporating a clamp which embraces adjacent ends of adjacent pipe lengths. The clamp is tightened onto a seal so that the coupling can withstand the maximum pressure the pipeline is designed to carry.
The clamp arrangement may hold the pipe lengths together by friction in low pressure situations, or may co-operate with a groove or shoulder formed at each end of each pipe length in higher pressure situations.
Such clamp arrangements may be fixed into position by bolting or over centre clamping.
A problem with known clamp arrangements is that it is difficult to ensure accurate alignment of the internal bores of adjacent pipe lengths, primarily due to the resilience of the seal which can allow adjacent pipe lengths to move radially relative to one another, such as may occur as the clamp is being tightened onto the pipe lengths.
A known method of overcoming this problem is to design the pipe lengths to have one male end and one female end. Joins between adjacent pipe lengths are then made between the male end of one pipe length and the female end of another pipe length. This allows adjacent pip ee located accurately relative to one another and leads to alignment of the bores of adjacent pipe lengths.
A disadvantage with this known system, however, is that the pipe lengths can only be fitted into the pipeline in one direction.
It has been proposed, in U.S. Pat. No. 3,836,159, to provide a sealing ring reacting between the ends of adjacent pipe lengths and comprising a resilient, deformable plastics component sandwiched between inner and outer retainer rings of metal such as steel which are resiliently deformable in a direction radially of the pipe lenths.
In such an arrangement, the pressure in the pipeline reacts primarily on the metal components of the seal.